A fun thing to do after screening Annihilation, writer/director Alex Garland’s intensely weird cinematic adaptation of Jeff VanderMeer’s intensely weird novel, is to eavesdrop as flattened audience members leaving the theatre hash over what they’ve just seen.

Was the movement of the water in the drinking glass at the end symbolic? Is the flora transmogrification a stand-in for environmental degradation? Was everybody just dreaming?

An alligator is not what it appears in Annihilation.

If there is such a thing as collective head-scratching in action, this is it. And most of that head-scratching is prompted by the film’s final 20 minutes, which are — no high-falutin’ film-speak here, kids — absolutely fucking bonkers.

Up to that point, Annihilation is fairly straightforward in a sci-fi/horror sort of way, and utterly stunning to watch. A group of military scientists headed by biologist Lena (Natalie Portman, fabulous) enter what’s called the Shimmer, which looks kind of like a giant soap bubble covering a huge swath of forest.

The Shimmer is swallowing up landscape faster than an urban condo developer, and whatever is going on inside seems nefarious from the outside. Previous groups of soldiers have gone in but never returned. Well, except for Lena’s husband (Oscar Isaac) but he returns a ruin.

With a crushing need to know, Lena joins four other scientists — Jennifer Jason Leigh, Gina Rodriguez, Tessa Thompson, Tuva Novotny — to explore inside the Shimmer. The film’s middle is its most heart-stopping, as the women explore a bizarre landscape where time evaporates, and plants and animals mutate and shape-shift. The less said about that the better (no spoilers here) but it’s equally magnificent and terrifying to witness.

“I've been re-working stories for over a quarter of a century and I am well used to the fact that most stories, including stories that I have written, are in effect re-tellings of other stories. It's a weird thing. It's sort of ritualistic, almost, I think. It's like a set of strange reassurances of what scares us or comforts us, and this story for me felt sort of outside that box.

“So just as a storyteller, that was immediately seductive and very interesting to me. It was incredibly powerful and unlike anything I've ever done before.”

Truth in advertising there. Some of Annihilation’s storytelling devices do recall (somewhat clunkily, the interrogation scenes) other films which may be necessary to help explain what’s happening on screen. But not much; this is as original a film as it’s possible to make and notably buoyed by a grandiose, yet really discomfiting score written by Portishead’s Geoff Barrow alongside composer Ben Salisbury. The film is also fearless in pursuing what can only be described as a scribbly narrative arc.

The take-aways are nevertheless significant. Its female leads feel exactly right and not just there as handy visual distraction as so often seems to be the case in sci-fi. No, the women are emblematic of the fearful, blazing life-force unfolding within the Shimmer. Or at least that’s what I was muttering as I left the theatre, scratching my head… but satisfied.